全文获取类型
收费全文 | 2368篇 |
免费 | 246篇 |
国内免费 | 2篇 |
出版年
2022年 | 29篇 |
2021年 | 81篇 |
2020年 | 28篇 |
2019年 | 41篇 |
2018年 | 46篇 |
2017年 | 56篇 |
2016年 | 75篇 |
2015年 | 115篇 |
2014年 | 106篇 |
2013年 | 141篇 |
2012年 | 151篇 |
2011年 | 162篇 |
2010年 | 108篇 |
2009年 | 107篇 |
2008年 | 127篇 |
2007年 | 99篇 |
2006年 | 97篇 |
2005年 | 92篇 |
2004年 | 72篇 |
2003年 | 79篇 |
2002年 | 63篇 |
2001年 | 44篇 |
2000年 | 42篇 |
1999年 | 42篇 |
1998年 | 26篇 |
1997年 | 17篇 |
1996年 | 24篇 |
1995年 | 14篇 |
1994年 | 15篇 |
1993年 | 22篇 |
1992年 | 38篇 |
1991年 | 32篇 |
1990年 | 39篇 |
1989年 | 43篇 |
1988年 | 27篇 |
1987年 | 28篇 |
1986年 | 29篇 |
1985年 | 22篇 |
1984年 | 23篇 |
1983年 | 17篇 |
1982年 | 22篇 |
1981年 | 14篇 |
1980年 | 16篇 |
1979年 | 21篇 |
1978年 | 21篇 |
1977年 | 17篇 |
1976年 | 10篇 |
1974年 | 11篇 |
1973年 | 9篇 |
1968年 | 10篇 |
排序方式: 共有2616条查询结果,搜索用时 78 毫秒
1.
Hugo R. Permingeat Maria V. Romagnoli Juliana I. Sesma Ruben H. Vallejos 《Plant Molecular Biology Reporter》1998,16(1):89-89
An easy, reproducible and fast procedure to isolate DNA from cotton leaves is described. The addition of 0.5 M glucose in the extraction buffer avoids browning by polyphenolic compounds and improves the quality of DNA for molecular analysis. The DNA yield ranged between 150–400 mg per gram of fresh tissue. The DNA was suitable for digestion by restriction enzymes and amplificatiion by Taq DNA polymerase. 相似文献
2.
3.
4.
5.
6.
7.
Dan Cog?lniceanu Laurentiu Rozylowicz Paul Székely Ciprian Samoil? Florina St?nescu Marian Tudor Diana Székely Ruben Iosif 《ZooKeys》2013,(341):49-76
The reptile fauna of Romania comprises 23 species, out of which 12 species reach here the limit of their geographic range. We compiled and updated a national database of the reptile species occurrences from a variety of sources including our own field surveys, personal communication from specialists, museum collections and the scientific literature. The occurrence records were georeferenced and stored in a geodatabase for additional analysis of their spatial patterns. The spatial analysis revealed a biased sampling effort concentrated in various protected areas, and deficient in the vast agricultural areas of the southern part of Romania. The patterns of species richness showed a higher number of species in the warmer and drier regions, and a relatively low number of species in the rest of the country. Our database provides a starting point for further analyses, and represents a reliable tool for drafting conservation plans. 相似文献
8.
9.
L Ruben 《The Journal of protozoology》1987,34(4):367-370
Calcium ions mediate cellular activity by binding to specific cellular proteins. The following study systematically examines the cellular complement of calcium-binding proteins in different cell fractions and life cycle stages of Trypanosoma brucei. Using a 45Ca-gel overlay procedure, eight calcium-binding proteins were consistently observed. The majority of proteins were cytosolic (84, 70, 64, 22, and 15 kd) while the remainder (55, 46, and 29 kd) were particulate. Although calmodulin was detected amongst the calcium-binding proteins, it did not represent the majority of calcium-binding activity. Of special interest was the 46 kd calcium-binding protein which was associated with 3-fold more calcium in cultured procyclic forms than in slender bloodstream forms. By contrast, promastigote forms of Leishmania mexicana did not contain the 46 kd calcium-binding protein. These data suggest that responsiveness to calcium signals may vary during the trypanosome life cycle as a result of changes in the cellular complement of calcium-binding proteins. 相似文献
10.
Is progesterone a pre-hormone in the CNS? 总被引:3,自引:0,他引:3
In this paper, experimental evidences have been presented indicating that progesterone per se appears to be a powerful modulatory steroid of presynaptic striatal dopaminergic terminals of the central nervous system of the rat. This effect of the progesterone signal is concentration as well as infusion mode dependent. Low pulsatile doses of the steroid positively modulate the mechanism by which dopamine terminals respond to amphetamine stimulation and increase tissue dopamine concentration. Whereas, continuous and/or high doses of this steroid negatively modulate the response of the dopamine terminals to amphetamine stimulation and decreases tissue dopamine concentration. This effects occurs through a membrane mediated mechanism either upon the dopamine neuron directly and/or upon an interneuron. Pregnanolone a 5- beta-3 beta-metabolite of progesterone known to activate the hypothalamic LHRH neural apparatus at the level of the hypothalamus of ovariectomized estrogen primed rats in both in vitro as well as in vivo preparations was completely ineffective at the level of the corpus striatum of similar animal preparations. Therefore, it is reasonable to assume that site specific mechanisms exist within the central nervous system which may control differentially the final action of progesterone. In the hypothalamus, pregnanolone appears to be the final signal for its action on the LHRH neural apparatus, whereas in the corpus striatum, the steroid per se, and dependent on the modality and/or the strength of the signal can either directly or indirectly up-regulate (stimulatory component) or down-regulate (inhibitory component) the activity of striatal dopaminergic terminals. 相似文献